The Collaborative International Dictionary of English v.0.48:
Rudder \Rud"der\, n. [OE. rother, AS. r[=o][eth]er a paddle;
akin to D. roer rudder, oar, G. ruder, OHG. roadar, Sw.
roder, ror, Dan. roer, ror. [root] 8. See Row to propel
with an oar, and cf. Rother. ]
1. (Naut.) The mechanical appliance by means of which a
vessel is guided or steered when in motion. It is a broad
and flat blade made of wood or iron, with a long shank,
and is fastened in an upright position, usually by one
edge, to the sternpost of the vessel in such a way that it
can be turned from side to side in the water by means of a
tiller, wheel, or other attachment.
2. Fig.: That which resembles a rudder as a guide or
governor; that which guides or governs the course.
For rhyme the rudder is of verses. --Hudibras.
3. In an aircraft, a surface the function of which is to
exert a turning moment about an axis of the craft.
[Webster 1913 Suppl.]
Balance rudder (Naut.), a rudder pivoted near the middle
instead of at the edge, -- common on sharpies.
Drop rudder (Naut.), a rudder extending below the keel so
as to be more effective in steering.
Rudder chain (Naut.), one of the loose chains or ropes
which fasten the rudder to the quarters to prevent its
loss in case it gets unshipped, and for operating it in
case the tiller or the wheel is broken.
Rudder coat (Naut.), a covering of tarred canvas used to
prevent water from entering the rudderhole.
Rudder fish. (Zool.)
(a) The pilot fish.
(b) The amber fish (Seriola zonata), which is bluish
having six broad black bands.
(c) A plain greenish black American fish (Leirus
perciformis); -- called also black rudder fish,
logfish, and barrel fish. The name is also applied
to other fishes which follow vessels.
Rudder pendants (Naut.), ropes connected with the rudder